Sheet transporting device

ABSTRACT

A roller shaft extends between a pair of frame walls. A feed roller is mounted on the roller shaft for feeding a stack of sheets placed on a feeding tray one by one from an uppermost sheet. A transmission gear is concentrically coupled to one end portion of the roller shaft to be rotated by driving of a driving motor. A boss extends axially inwardly from a center position of the transmission gear. The roller shaft has a flat key portion at the one end portion thereof. The flat key portion has a substantially D-shape in cross section. The flat key portion is coupled to the boss by being received in a non-circular hole of the boss. With this arrangement, an eccentric displacement of the roller shaft relative to the transmission gear is suppressed, and the feed roller is easily detachable from the roller shaft with a simplified operation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a sheet transporting device incorporated with a roller shaft mounting structure, which is applicable to a sheet feeding device for feeding sheets one by one into a main body of an image forming apparatus. The sheet transporting device is applicable to image forming apparatuses such as copiers, facsimile machines, and printers.

[0003] 2. Description of the Related Art

[0004] Heretofore, there has been known a sheet feeding device 90 as shown in FIGS. 8A, 8B, and 8C, as disclosed in Japanese Examined Utility Model Publication No. 6-43071. FIG. 8A is a side view, and FIG. 8B is a front view, respectively showing essential parts of the sheet feeding device 90. FIG. 8C is an enlarged perspective view showing an attachment structure 96 which makes it possible for an operator to detachably attach a roller shaft 921.

[0005] The sheet feeding device 90 is adapted to feed sheets P one by one from a sheet cassette 91 provided in an image forming apparatus such as a copier into the image forming apparatus. As shown in FIG. 8A, the sheet feeding device 90 includes feed rollers 92 which are rotated about an axis of the roller shaft 921 together with the roller shaft 921, a guide plate 93 for guiding the document sheet P dispensed from the sheet cassette 91 by the feed rollers 92, and a pair of upper and lower registration rollers 94 which are disposed at a downstream end of the guide plate 93 in the sheet feeding direction. The feed rollers 92 are arranged at such a position as to come into contact with the uppermost document sheet P in the sheet cassette 91. The document sheet P dispensed from the sheet cassette 91 as timed with a rotation of the feed rollers 92 is fed between the registration roller pair 94 while being supported on the guide plate 93, and is transported into the image forming apparatus by rotation of the registration roller pair 94.

[0006] It is necessary to detach the feed rollers 92 from a pair of support frames 95 which support the roller shaft 921 extending in a widthwise direction of the image forming apparatus, as shown by the two-dotted-chain line shown in FIG. 8B, in order to carry out maintenance service such as replacement and cleaning of parts of the sheet feeding device 90. For this purpose, the attachment structure 96 as shown in FIG. 8C is provided at an end portion of the roller shaft 921.

[0007] The attachment structure 96 includes a coupling cylinder 961, a roller shaft end portion 962, and a compression coil spring 963. The coupling cylinder 961 is mounted on a driving shaft 97 to be axially movable but non-rotatable together with the driving shaft 97. The driving shaft 97 is passed through the support frames 95 concentrically with the roller shaft 921. The roller shaft end portion 962 is detachably mounted in the coupling cylinder 961, and is non-rotatable together with the coupling cylinder 961. The compression coil spring 963 is wound around the driving shaft 97 between the coupling cylinder 961 and the support frame 95. A drive gear 98 is fixedly mounted at a base end portion of the driving shaft 97 to transmit a driving force of a drive source (not shown) to the driving shaft 97.

[0008] An engaging pin 971 radially outwardly extends from a lead end of the driving shaft 97. A cutaway groove 964 is formed in parallel to an axial direction of the coupling cylinder 961 from an opening end thereof toward a base end thereof. Engagement of the engaging pin 971 in the cutaway groove 964 makes it possible to reciprocate the coupling cylinder 961 in the axial direction thereof while keeping the coupling cylinder 961 non-rotatable together with the driving shaft 97.

[0009] An engaging pin 965 extends radially between the opposing inner circumferential surfaces of the coupling cylinder 961 near the opening end thereof. A cutaway groove 966 is formed in the roller shaft end portion 962 to be engageable with the engaging pin 965. Engagement of the engaging pin 965 in the cutaway groove 966 with the roller shaft end portion 962 being received in the coupling cylinder 961 makes it possible to couple the roller shaft 921 to the driving shaft 97, so that the roller shaft 921 is rotatable together with the driving shaft 97 via the coupling cylinder 961.

[0010] In the attachment structure 96 having the above construction, when an operator wishes to detach the feed rollers 92 from the support frames 95, the operator can detach the roller shaft end portion 962 from the coupling cylinder 961 by sliding the coupling cylinder 961 toward the base end of the driving shaft 97 (leftward in FIG. 8B) against a resilient force of the compression coil spring 963, as shown by the arrow in FIG. 8B. This arrangement enables the operator to easily detach the roller shaft 921 without disassembling the sheet feeding device 90 such as loosening a screw which fastens the support frame 95 to the apparatus main body.

[0011] The attachment structure 96 as disclosed in Japanese Examined Utility Model Publication No. 6-43071 has suffered from a drawback that the number of parts is increased due to necessity of providing additional parts such as the engaging pin 971 for the driving shaft 97, and the engaging pin 965, as well as the driving shaft 97, the coupling cylinder 961, and the compression coil spring 963. As a result, the costs relating to the parts and assembling of the parts are raised.

[0012] Further, the driving shaft 97 and the roller shaft 921 are coupled to each other by way of the coupling cylinder 961 which is axially movable, in other words, which may not provide sufficient force to securely couple the driving shaft 97 and the roller shaft 961 concentrically with each other. Accordingly, the driving shaft 97 and the roller shaft 921 are likely to be eccentrically displaced from each other. In order to solve this problem, it is necessary to improve precision in processing, which raises another problem that the processing cost may be raised.

SUMMARY OF THE INVENTION

[0013] In view of the above, it is an object of the present invention to overcome the problems residing in the prior art. It is another object of the present invention to provide a simple-structured sheet transporting device incorporated with a roller shaft mounting structure that enables to suppress eccentric displacement of the roller shaft and to facilitate attaching/detaching operation of a feed roller.

[0014] According to an aspect of the present invention, a sheet transporting device is used in an image forming apparatus. The sheet transporting device includes a pair of frame walls, a roller shaft extending between the frame walls, a feed roller mounted on the roller shaft for feeding sheets stacked on a sheet stacking portion of the image forming apparatus one by one from an uppermost sheet, and a transmission gear provided at an outer side of one of the frame walls for transmitting a driving force to the roller shaft.

[0015] The sheet transporting device is provided with an attachment structure mounted on the roller shaft. The attachment structure includes a boss to be received in a hole of the frame wall. The boss is formed with a non-circular hole. An engaging end portion is formed in an end portion of the roller shaft, and has such a configuration as to be received in the non-circular hole of the boss in a non-rotatable state relative to the transmission gear.

[0016] These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description along with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a perspective view showing an example of a copier to which a sheet transporting device in accordance with an embodiment of the present invention is applied.

[0018]FIG. 2 is a perspective view seen from a left side of the sheet transporting device, showing a document sheet feeding section of the copier with a top wall and a rear wall not being illustrated to explain a mounted state of the sheet transporting device.

[0019]FIG. 3 is a perspective view seen from a right side of the sheet transporting device, showing the document sheet feeding section of the copier with the top wall and the rear wall not being illustrated to explain the mounted state of the sheet transporting device.

[0020]FIGS. 4A and 4B are perspective views showing the sheet transporting device which is mounted on the document sheet feeding section of the copier, wherein FIG. 4A shows a state that a document sheet feeding unit is detached from a driving unit, and FIG. 4B shows a state that the document sheet feeding unit has been attached to the driving unit.

[0021]FIGS. 5A and 5B are perspective views showing an embodiment of a transmission gear, wherein FIG. 5A shows a state immediately before a flat key portion of a roller shaft is being received in a non-circular hole of a boss of the transmission gear, and FIG. 5B shows a state that the flat key portion has been received in the non-circular hole.

[0022]FIGS. 6A, 6B, 6C, and 6D are illustrations for explaining operations of the sheet transporting device, wherein FIG. 6A shows a state that a hemispherical portion of the roller shaft is about to be received in an insertion hole of a left-side frame wall, FIG. 6B shows a state that the hemispherical portion of the roller shaft has been received in the insertion hole, followed by mounting of a second bearing in the insertion hole, and also shows a state that the flat key portion opposes a circular hole of a first bearing which is mounted in an insertion hole of a right-side frame wall while being mounted on the boss of the transmission gear, FIG. 6C shows a state that the flat key portion is received in the circular hole of the first bearing, and FIG. 6D shows a state that a stopper ring is mounted in a cutaway groove of the roller shaft.

[0023]FIGS. 7A, 7B, and 7C are cross-sectional views showing a modification as to how a roller shaft is coupled to a transmission gear, wherein FIG. 7A shows a state that a coil spring is dismounted from the transmission gear, FIG. 7B shows a state that a bearing is mounted in an insertion hole after a hemispherical portion of a roller shaft is received in the insertion hole, with a flat key portion opposing a non-circular hole of the transmission gear, and FIG. 7C shows a state that the roller shaft is coupled to the transmission gear via the coil spring.

[0024]FIGS. 8A, 8B, and 8C are illustrations showing a conventional sheet feeding device, wherein FIGS. 8A and 8B are side view and a front view respectively showing essential parts of the sheet feeding device, and FIG. 8C is an exploded perspective view showing an attachment structure of detachably attaching a roller shaft.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025]FIG. 1 is a perspective view showing an example of a copier to which a sheet transporting device in accordance with an embodiment of the present invention is applied. As shown in FIG. 1, the copier (image forming apparatus) 10 is constructed in such a manner that a cover member 12 provided with a document sheet feeding mechanism is mounted on a top of a box-like apparatus main body 11.

[0026] The apparatus main body 11 is internally provided with an optical system (not shown) for reading an image of a document sheet fed by the document sheet feeding mechanism, a developing section (not shown) provided with a photosensitive drum, a developing device, and the like to transfer the document image read by the optical system onto a copy sheet as a toner image, a fixing section (not shown) provided with a pair of fixing rollers, and the like to fix the transferred toner image on the sheet, and a sheet feeding section (not shown) provided with a sheet cassette and the like to store a stack of copy sheets therein.

[0027] A sheet fed by the sheet feeding section is fed to the developing section via a predetermined transport path. Then, an electrostatic latent image is formed on a circumferential surface of the photosensitive drum based on the image data read by the optical system, and the latent image is developed to a toner image by supply of toner from the developing device, whereby the toner image is transferred onto the sheet. After the image development, the transferred toner image is fixed on the sheet by thermal fixation by the fixing roller pair, and the sheet carrying the fixed toner image is discharged onto a sheet discharging section (not shown) provided at a side portion of the apparatus main body 11.

[0028] The cover member 12 is provided with a document sheet feeding section 13 at a side portion thereof for feeding a document sheet. The cover member 12 is further provided with a document sheet feeding tray (sheet stacking portion) 14 extending obliquely upwardly from the document sheet feeding section 13 toward the other end of the cover member 12 opposite to the document sheet feeding section 13, and a document sheet discharging tray 15 which is disposed below the document sheet feeding tray 14 and substantially extends over the entire surface of the cover member 12. A pair of document sheet alignment members 141 are provided at a base portion (left side in FIG. 1) of the document sheet feeding tray 14 to align the document sheets placed on the document sheet feeding tray 14 in a widthwise direction of the apparatus main body 11. The document sheets on the document sheet feeding tray 14 are aligned in the widthwise direction of the apparatus main body 11 by regulating the inner distance between the pair of document sheet alignment members 141.

[0029] The document sheet feeding section 13 is constructed in such a manner that the sheet transporting device 20 (see FIG. 2) according to the embodiment of the present invention is housed in a space defined by a pair of frame walls 131 opposed to each other in the widthwise direction of the apparatus main body 11, a top wall 132 which is pivotally opened and closed while being supported on upper ends of the frame walls 131, and a rear wall 133 which extends between the frame walls 131 and covers a space opposite to the document sheet feeding tray 14. A document sheet feeding port 135 is defined by the pair of frame walls 131, and the top wall 132, and is formed opposite to the rear wall 133. Document sheets placed on the document sheet feeding tray 14 are successively fed into the document sheet feeding section 13, which will be described later.

[0030] A stack of document sheets placed on the document sheet feeding tray 14 with their respective lateral ends thereof aligned by the document sheet alignment members 141 are fed into the document sheet feeding section 13 one by one by driving the sheet transporting device 20, whereby the image of each document sheet is read by the optical system (not shown).

[0031]FIGS. 2 and 3 are perspective views showing the document sheet feeding section 13 with the top wall 132 and the rear wall 133 not being illustrated to explain the mounted state of the sheet transporting device 20. FIG. 2 is a diagram viewed from a left side of the apparatus main body 11, and FIG. 3 is a diagram viewed from a right side of the apparatus main body 11. FIGS. 4A and 4B are perspective views of the sheet transporting device 20 which is to be installed in the document sheet feeding section 13. FIG. 4A shows a state that a document sheet feeding unit is detached from a driving unit, and FIG. 4b shows a state that the document sheet feeding unit has been attached to the driving unit.

[0032] As shown in FIGS. 2, 3, 4A, and 4B, the sheet transporting device 20 includes the document sheet feeding unit 30 for successively feeding document sheets P placed on the document feeding tray 14 into the apparatus main body 11, and the driving unit 60 for driving the document sheet feeding unit 30.

[0033] The document sheet feeding unit 30 includes a roller shaft 31 extending between the pair of frame walls 131, a casing 40 pivotally mounted on an intermediate portion of the roller shaft 31, a feed roller unit 50 supported on the casing 40, and a pair of stopper members 39 attached to the feed roller unit 50. As shown in FIGS. 2 and 3, the roller shaft 31 extends between the frame walls 131 at a position slightly downstream (left side in FIG. 2, right side in FIG. 3) relative to the document sheet alignment members 141. As shown in FIGS. 4A and 4B, the roller shaft 31 includes a shaft main body 32, a flat key portion 33 formed at a right-end portion of the shaft main body 32 in FIG. 4A, and a cutaway groove 34 formed in a left-end portion thereof.

[0034] The flat key portion (engaging end portion) 33 is formed to detachably mount a one end portion (right-end portion in FIG. 4A) of the roller shaft 31 to the driving unit 60 by way of a bearing unit 21. The cutaway groove 34 is formed to mount a stopper ring (stopper piece) 22 in the other end portion (left-end portion in FIG. 4A) of the roller shaft 31 by way of the bearing unit 21 to keep the roller shaft 31 from coming off the frame walls 131.

[0035] The bearing unit 21 includes a first bearing 211 for receiving the flat key portion 33 formed at the right-end portion of the roller shaft 31 in FIG. 4A, and a second bearing 212 for receiving the left-end portion of the roller shaft 31 in FIG. 4A. The first bearing 211 (second bearing 212) has such an outer dimension as to be slidably received in an insertion hole 134 of the corresponding frame wall 131, which will be described later. A circular hole 213 is formed in the center of the first bearing 211 to receive a boss 642 of a transmission gear 64.

[0036] A bearing hole 214 having a circular shape in cross section is formed in the center of the second bearing 212 with such an inner dimension as to slidably receive the roller shaft 31. Specifically, the bearing hole 214 has a bell-like shape such that the inner dimension thereof is axially outwardly decreased from the opening of the second bearing 212. The bearing hole 214 has the bell-like shape to easily receive the roller shaft 31 which is to be tiltingly inserted through the second bearing 212 (see FIG. 6A). The shape of the bearing hole 214 is not limited to the bell-like shape. Alternatively, the bearing hole 214 may have a constant inner dimension over the entirety of the axial direction of the hole.

[0037] A hemispherical portion 35 is formed at an end portion of the roller shaft 31 where the cutaway groove 34 is formed. The hemispherical portion 35 also facilitates inserting the end portion of the roller shaft 31 through the second bearing 212. The shape of the end portion of the roller shaft 31 is not limited to the hemispherical shape. Forming a radially cutaway portion in the end portion of the roller shaft 31 enables to support the roller shaft 31 in the second bearing 212.

[0038] The insertion hole 134 is formed in each of the frame walls 131 to support the roller shaft 31 (see FIGS. 6A through 6D). Each of the insertion holes 134 has such a size and a shape as to receive the bearing unit 21 (namely, the first bearing 211 and the second bearing 212) in a non-rotatable state.

[0039] The casing 40 is provided to support the feed roller unit 50, and includes a top wall 41, and a pair of side walls 42 opposing to each other in the widthwise direction of the apparatus main body 11. The side walls 42 are formed by bending side portions of the top wall 41 downward. The casing 40 is mounted on the roller shaft 31 by passing the roller shaft main body 32 through the side walls 42. A cross shaft 43 is formed on each of the side walls 42 at a forward side of the roller shaft main body 32, namely, on the side of the document sheet alignment members 141, as shown in FIG. 2, to support the stopper members 39.

[0040] The casing 40 is pivotally rotatable between a sheet feeding state where an upstream end thereof (right side in FIG. 2) relative to the roller shaft 31 is lowered to such a position as to feed the uppermost document sheet P, and a retracted state where the upstream end is lifted upward and retracted. While the casing 40 is set to the retracted state, the document sheet P is placed on the document sheet feeding tray 14.

[0041] The stopper members 39 are pivotally rotatable about an axis of the cross shaft 43 while the casing 40 is set to the sheet feeding state. With this arrangement, the document sheet P placed on the document sheet feeding tray 14 is allowed to pass under the casing 40. On the other hand, when the casing 40 is set to the retracted state, a projection 391 formed on an upper portion of each stopper member 39 engages an engaging recess (not shown) formed in the underside of the top wall 132 of the document sheet feeding section 13, whereby the casing 40 is held in the retracted state, and the feed roller unit 50 is securely supported on the casing 40.

[0042] The feed roller unit 50 is adapted to feed the sheets P placed on the document sheet feeding tray 14 one by one into the apparatus main body 11, after confirming that each document sheet P is securely placed on the document sheet feeding tray 14 with its lateral ends thereof being aligned by the document sheet alignment members 141, and with its lead end thereof being pressingly held by the pair of downwardly-oriented stopper members 39 (see FIGS. 2 and 3). As shown in FIGS. 4A and 4B, the feed roller unit 50 includes a feed roller 51 which is mounted concentrically with the roller shaft main body 32 between the side walls 42 of the casing 40, and a pickup roller 52 which is provided at an upstream side relative to the feed roller 51 (forward side on the plane of FIGS. 4A and 4B) between the side walls 42. The pickup roller 52 is rotatably supported about an axis of a pickup roller shaft 53 extending between the side walls 42.

[0043] The pickup roller shaft 53 is arranged at such a position that the surface of the pickup roller 52 comes into contact with the uppermost document sheet P in a state that the stack of sheets P placed on the document sheet feeding tray 14 are temporarily held by the stopper members 39. With this arrangement, the uppermost document sheet P is fed toward the feed roller 51 aided by the rotation of the pickup roller 52. The document sheet P picked up by the pickup roller 52 is fed into the document sheet feeding section 13 by rotation of the downstream-located feed roller 51.

[0044] As shown in FIGS. 4A and 4B, a feed roller gear 54 concentrically rotated with the roller shaft main body 32 is provided at the right side of the feed roller 51 in the casing 40, and a pickup roller gear 55 is provided at the right side of the pickup roller 52 to be rotatable about an axis of the pickup roller shaft 53. An intermediate gear 56 is provided between the pickup roller gear 55 and the feed roller gear 54. With this arrangement, the feed roller 51 and the pickup roller 52 are rotated together in the same direction (clockwise direction in the example of FIGS. 2, 4A, and 4B) to feed the document sheet P inside the document sheet feeding section 13.

[0045] A one-way clutch is provided each between the feed roller 51 and the feed roller gear 54, and between the pickup roller 52 and the pickup roller gear 55. The one-way clutch is provided to rotate the feed roller 51 and the pickup roller 52 together with the gears 54, 55, respectively, while the feed roller gear 54 and the pickup roller gear 55 are rotated forward (clockwise) to feed the document sheet P inside the document sheet feeding section 13, and to keep the feed roller 51 and the pickup roller 52 from being rotated together with the gears 54, 55, respectively, while the feed roller gear 54 and the pickup roller gear 55 are rotated backward (counterclockwise).

[0046] In the embodiment of the present invention, when a sensor (not shown) detects the document sheet P when the document sheet P fed by the feed roller 51 reaches a pair of registration rollers (not shown) provided in a rear part of the document sheet feeding section 13, the driving unit 60 is driven reversely, based on the detection signal, to rotate the registration roller pair forward and to rotate the roller shaft 31 backward. The one-way clutch is provided to prevent the document sheet P which has been fed into the document sheet feeding section 13 by the forward rotation of the feed roller 51 from being exerted with a force acting backward when the roller shaft 31 is rotated backward.

[0047] The driving unit 60 is adapted to supply a rotating force to the roller shaft 31, and is fixedly mounted to an outer side of the frame wall 131 (right side in FIG. 2, left side in FIG. 3). As shown in FIGS. 4A and 4B, the driving unit 60 includes a driving motor 62 which is fixedly attached to the outer side of the frame wall 131 with a support plate 61 interposed therebetween, and a gear group 63 provided on the inner side of the frame wall 131.

[0048] The gear group 63 includes: a driving gear 631 concentrically and integrally rotated with an output shaft 621 of the driving motor 62; a first driven gear 632 meshed with the driving gear 631; a second driven gear 633 meshed with the first driven gear 632; a transmission gear 64 meshed with the second driven gear 633 to transmit the rotating force of the driving motor 62 to the roller shaft 31; a third driven gear 634 which is concentrically and integrally rotated with the first driven gear 632 and has a diameter larger than that of the first driven gear 632; and a registration gear 65 meshed with the third driven gear 634 via a small gear. The registration gear 65 is coupled to a registration roller (not shown) via a one-way clutch (not shown), and is so constructed as to transmit the rotation of the registration gear 65 to the registration roller only while the driving motor 62 is rotated backward.

[0049]FIGS. 5A and 5B are perspective views showing the transmission gear 64. FIG. 5A shows a state immediately before the flat key portion 33 of the roller shaft 31 is being received in a non-circular hole 643 of the boss 642 of the transmission gear 64. FIG. 5B shows a state that the flat key portion 33 is received in the non-circular hole 643. As shown in FIGS. 5A and 5B, the transmission gear 64 includes a gear body 641 meshed with the second driven gear 633, and the boss 642 which is formed concentrically with the gear body 641 and protrudes axially inwardly in the document sheet feeding section 13. The non-circular hole (non-deformable hole) 643 substantially having a D-shape in cross section is formed in an end portion of a transmission shaft, so that the flat key portion 33 of the roller shaft 31 is fittingly received in the non-circular hole 643. The roller shaft 31 is coupled to the transmission gear 64 to be rotatable with the boss 642 when the flat key portion 33 is received in the non-circular hole 643.

[0050] In the sheet transporting device 20 having the above construction, as shown in FIG. 4B, an operator can attach the roller shaft 31 to the driving unit 60 by passing the hemispherical portion 35 of the roller shaft 31 through the second bearing 212, mounting the second bearing 212 in the insertion hole 134 of the left-side frame wall 131, temporarily moving the roller shaft 31 leftward, followed by moving the roller shaft 31 rightward, and then inserting the flat key portion 33 in the non-circular hole 643 of the boss 642 supported on the first bearing 211. Likewise, the operator can detach the roller shaft 31 from the driving unit 60 by implementing the above steps in the reverse order.

[0051] In the following, the operation of the sheet transporting device is described referring to FIGS. 6A through 6D. FIG. 6A shows a state that the hemispherical portion 35 of the roller shaft 31 is about to be received in the insertion hole 134 of the left-side frame wall 131. FIG. 6B shows a state that the second bearing 212 is mounted in the insertion hole 134 after the hemispherical portion 35 of the roller shaft 31 is received in the insertion hole 134, and that the flat key portion 33 is opposed to the boss 642 of the transmission gear 64. FIG. 6C shows a state that the flat key portion 33 is received in the circular hole 213 of the boss 642. FIG. 6D shows a state that the stopper ring 22 is mounted in the cutaway grove 34 of the roller shaft 31.

[0052] In mounting the document sheet feeding unit 30 between the pair of frame walls 131 of the document sheet feeding section 13, as shown in FIG. 6A, first, an operator attaches the second bearing 212 to the end portion of the roller shaft 31 where the cutaway groove 34 is formed. Then, the operator inserts the end portion of the roller shaft 31 into the insertion hole 134 while holding the roller shaft 31 tiltingly. After confirming that the flat key portion 33 of the roller shaft 31 does not interfere with the right-side frame wall 131, the operator holds the roller shaft 31 horizontally, and mounts the second bearing 212, as shown in the two-dotted-chain line in FIG. 6B, in the insertion hole 134 of the left-side frame wall 131 by sliding the second bearing 212 toward the left-side frame wall 131, as shown by the leftward arrow in FIG. 6B, while keeping the horizontal state of the roller shaft 31.

[0053] Next, the operator holds the roller shaft 31 in such a manner that the flat key portion 33 opposes the non-circular hole 643 of the boss 642, and then moves the roller shaft 31 toward the circular hole 213, as shown by the rightward arrow in FIG. 6B. Thereby, as shown in FIG. 6C, the flat key portion 33 of the roller shaft 31 is received in the non-circular hole 643 of the boss 642.

[0054] Then, when the operator mounts the stopper ring 22 in the cutaway groove 34 of the roller shaft 31, as shown by the arrow in FIG. 6C, the roller shaft 31 is kept from moving leftward in FIGS. 6A through 6D. Thus, as shown in FIG. 6D, the document sheet feeding unit 30 is mounted between the pair of frame walls 131 while being kept from coming off the frame walls 131.

[0055] The sheet transporting device 20 can be detached from the document sheet feeding section 13 of the copier 10 by implementing the above steps in the reverse order.

[0056] As mentioned above in detail, the sheet transporting device 20 according to the embodiment of the present invention is applicable to the copier 10, for instance. The sheet transporting device 20 is constructed in such a manner that the roller shaft 31 is mounted between the pair of frame walls 131 with the feed roller 51 mounted thereon for successively feeding the document sheets placed on the document sheet feeding tray 14 from the uppermost one, the transmission gear 64 is concentrically coupled to the roller shaft 31 at the one end of the roller shaft 31, so that the roller shaft 31 is rotatable by driving of the driving motor 62, the boss 642 projects from the center position of the transmission gear 64, the roller shaft 31 is formed with the flat key portion 33 which is to be concentrically and detachably inserted in the non-circular hole 643 of the boss 642, and the cutaway groove 34 is formed in the end portion of the hemispherical portion 35 for detachably receiving the stopper ring 22. This arrangement enables the operator to implement the steps of: mounting the hemispherical portion 35 of the roller shaft 31 in the insertion hole 134 of the frame wall 131 before mounting the stopper ring 22; mounting the second bearing 212 in the insertion hole 134 after confirming that the flat key portion 33 does not interfere with the transmission gear 64; inserting the flat key portion 33 in the non-circular hole 643 of the boss 642 of the transmission gear 64; and mounting the stopper ring 22 in the cutaway groove 34 of the roller shaft 31. When these steps are conducted, the roller shaft 31 is mounted between the pair of frame walls 131 without likelihood that the roller shaft 31 comes off the frame walls 131.

[0057] In detaching the roller shaft 31 from the pair of frame walls 131, after detaching the stopper ring 22 from the roller shaft 31, the operator moves the roller shaft 31 axially outwardly from the frame wall 131 where the hemispherical portion 35 of the roller shaft 31 is mounted, and tiltingly holds the roller shaft 31 to avoid interference of the flat key portion 33 with the frame wall 131 after confirming that the flat key portion 33 of the roller shaft 31 has left from the non-circular hole 643 of the boss 642 of the transmission gear 64. Thus, the operator is prepared to detach the roller shaft 31 from the pair of frame walls 131.

[0058] While the roller shaft 31 is mounted between the pair of frame walls 131, the roller shaft 31 is integrally rotated with the transmission gear 64 with the flat key portion 33 being received in the insertion hole 134. With this arrangement, the driving force of the drive source is securely transmitted to rotate the feed roller 51 about an axis of the roller shaft 31 via the transmission gear 64 and the roller shaft 31. Thereby, the sheets P placed on the sheet stacking portion 14 are fed one by one into the document sheet feeding section 13.

[0059] In this way, the rotation of the transmission gear 64 is directly conveyed to the roller shaft 31 without providing a coupling cylinder between the transmission gear 64 and the roller shaft 31, which has been required in the conventional arrangement. This arrangement enables to securely convey the rotation of the transmission gear 64 to the roller shaft 31 without eccentric displacement of the roller shaft 31 relative to the transmission gear 64 and to effectively prevent occurrence of a feeding-related trouble due to eccentric rotation of the feed roller 51.

[0060] Further, the above arrangement eliminates necessity of using a coupling member such as the conventional coupling cylinder, and urging means such as a coil spring for exerting an urging force to the coupling member. Thereby, the number of the parts can be reduced, and the roller shaft 31 can be detachably attached to the frame members with a simplified operation.

[0061] The coupling mechanism in accordance with the embodiment of the present invention has a simplified construction, namely, comprises the boss 642 which projects from the end surface of the transmission gear 64, the non-circular hole 643 formed in the boss 642, and the flat key portion 33 formed on the end portion of the roller shaft 31. This arrangement contributes to reduction in costs relating to the parts and the processing, and makes it possible for an operator to detachably attach the roller shaft 31 to the transmission gear 64 by merely inserting the flat key portion 33 in the non-circular hole 643, thereby providing improved operability to the operator.

[0062] Furthermore, the cutaway groove 34 is formed in the end portion of the roller shaft 31, and the stopper ring 22 is mounted in the cutaway groove 34. This arrangement keeps the roller shaft 31 from coming off the frame walls 131, namely, keeps the stopper ring 22 from moving beyond the adjoining frame wall 131 because the stopper ring 22 is mounted in the cutaway groove 34 of the roller shaft 31 after the second bearing 212 is mounted on the roller shaft 31. This arrangement securely prevents the roller shaft 31 from coming off the frame walls 131.

[0063] The roller shaft 31 can be detached from the pair of frame walls 131 by detaching the stopper ring 22 from the roller shaft 31. Namely, the operator is allowed to axially move the roller shaft 31 by detaching the stopper ring 22 from the roller shaft 31, and thus is allowed to detach the roller shaft 31 from the frame walls 131.

[0064] The present invention is not limited to the foregoing embodiment, and the following modifications and alterations are applicable.

[0065] In the foregoing embodiment, the stopper ring 22 is mounted in the cutaway groove 34 formed in the roller shaft 31 to keep the roller shaft 31 from coming off the frame walls 131. Alternatively, the roller shaft 31 may be formed with a through hole, and a stopper pin may be inserted in the through hole.

[0066] In the foregoing embodiment, the flat key portion 33 having a substantially D-shape in cross section is formed on the one end portion of the roller shaft 31, the boss 642 projecting from the center position of the transmission gear 64 is formed, and the non-circular hole 643 having such a shape as to fittingly receive the flat key portion 33 is formed in the boss 642 so as to integrally rotate the roller shaft 31 with the transmission gear 64. The cross-sectional shape of the flat key portion 33 and the non-circular hole 643 is not limited to the substantially D-shape. As far as the roller shaft 31 and the transmission gear 64 are integrally rotatable about the axis of the roller shaft 31, any shape including a polygonal shape may be applicable to the flat key portion 33 and the non-circular hole 643.

[0067] In the foregoing embodiment, the copier 10 is shown as an example of the apparatus to which the inventive sheet transporting device 20 is applied. Alternatively, the present invention is applicable to image forming apparatuses such as facsimile machines and printers.

[0068] As shown in cross-sectional views of FIGS. 7A through 7C, there is proposed a modified coupling mechanism of a roller shaft and a transmission gear. FIG. 7A shows a state that a coil spring is detached from the transmission gear, FIG. 7B shows a state that the coil spring is mounted on the transmission gear, and FIG. 7C shows a state that the roller shaft is coupled to the transmission gear via the coil spring.

[0069] In the modification, a flat key portion is not formed at an end portion of the roller shaft 31. Specifically, the roller shaft 31 has a circular cylinder 36 which is concentric with a roller shaft main body 32 and has substantially the same diameter as the roller shaft main body 32. The circular cylinder 36 corresponds to the end portion (flat key portion) of the roller shaft 31 in the foregoing embodiment. The circular cylinder 36 does not necessarily have the same diameter as the roller shaft main body 32, but may have a smaller diameter than the roller shaft main body 32.

[0070] A circular recess 644 is formed in an end surface of a boss 642 of the transmission gear 64. The circular recess 644 has an inner diameter larger than an outer diameter of the circular cylinder 36. With this arrangement, there is defined an annular clearance between the circular cylinder 36 and the circular recess 644 when the circular cylinder 36 is received in the circular recess 644. The coil spring 66 having such a dimension as to fit in the annular clearance is mounted in the circular recess 644, as shown in FIG. 7B. In this modification, the coil spring 66 is formed by processing a drawn wire having a polygonal shape in cross section into a helical spring.

[0071] In the coupling mechanism having the above construction, the coil spring 66 is tightly wound around the circular cylinder 36, as the transmission gear 64 is driven in such a direction as to wind up the coil spring 66. Thereby, the rotation of the transmission gear 64 is conveyed to the roller shaft 31. On the other hand, as the transmission gear 64 is driven in such a direction as to loosen the coil spring 66, transmission of the rotation of the transmission gear 64 to the circular cylinder 36 is stopped. Thereby, the rotation of the roller shaft 31 is suspended despite the rotation of the transmission gear 64.

[0072] In this way, the coil spring 66 provided between the circular recess 644 and the circular cylinder 36 serves as a one-way clutch. Winding the coil spring 66 in such a direction as to rotate the roller shaft 31 exclusively in the direction to feed the document sheet P into the document sheet feeding section 13 eliminates a drawback that the roller shaft 31 is rotated backward accompanied by backward rotation of the transmission gear 64. With this arrangement, there is avoided a possibility that the document sheet P may be fed backward accompanied by backward rotation of the feed roller via the roller shaft 31.

[0073] As described above, an inventive sheet transporting device for use in an image forming apparatus comprises: a pair of frame walls opposed to each other; a roller shaft extending between the frame walls, opposite end portions of the roller shaft being received in insertion holes formed in the frame walls, respectively; a feed roller which is mounted on the roller shaft and is rotatable about an axis of the roller shaft, the feed roller for feeding sheets stacked on a sheet stacking portion of the image forming apparatus one by one from an uppermost sheet; a transmission gear which is provided at an outer side of one of the frame walls, the transmission gear having a center position opposed to the insertion hole of the frame wall; and an attachment structure which is so configured as to mount the roller shaft between the frame walls so as to transmit a driving force of the transmission gear to the roller shaft.

[0074] The attachment structure includes a boss which is formed co-axially with the transmission gear and projects in the axial direction of the roller shaft to be received in the insertion hole of the frame wall, the boss being formed with a non-circular hole extending in the axial direction of the roller shaft; and an engaging end portion which is formed in an end portion of the roller shaft and has such a configuration as to be received in the non-circular hole of the boss in a non-rotatable state relative to the transmission gear.

[0075] In the above arrangement, the roller shaft is mounted between the frame walls when an operator implements the steps of: while tiltingly holding the roller shaft, inserting the other end portion of the roller shaft, which is opposite to the one end portion of the roller shaft where a flat key portion (engaging end portion) is formed, in the corresponding insertion hole of the frame wall after confirming that the engaging end portion of the roller shaft does not interfere with the frame wall; and inserting the engaging end portion of the roller shaft in the non-circular hole of the boss of the transmission gear.

[0076] On the other hand, the roller shaft is detached from the frame walls when the operator implements the steps of: moving the roller shaft axially, so that the other end portion of the roller shaft is away from the frame wall; holding the roller shaft tiltingly to avoid interference with the frame wall in a state that the engaging end portion of the roller shaft is away from the frame wall; and withdrawing the roller shaft to disengage the engaging end portion from the insertion hole of the frame wall.

[0077] Since the roller shaft is integrally rotated with the transmission gear about the axis of the transmission gear by the operation of the coupling mechanism in a state that the roller shaft extends between the frame walls, the driving force of the drive source is transmitted to the feed roller to rotate the feed roller about the axis of the roller shaft via the transmission gear and the roller shaft. With this arrangement, the sheets stacked on the sheet stacking portion are fed successively.

[0078] The rotation of the transmission gear is directly transmitted to the roller shaft without providing an additional coupling member such as a coupling cylinder and a stopper pin between the roller shaft and the transmission gear, which has been required in the conventional arrangement. This arrangement is advantageous in transmitting the rotation of the transmission gear to the roller shaft without eccentric displacement of the roller shaft relative to the transmission gear, and in effectively preventing occurrence of a feeding-related trouble due to eccentric rotation of the feed roller.

[0079] Further, since the coupling mechanism has a simplified construction, as compared with the conventional arrangement, the above arrangement contributes to reduction in the number of parts, and secures improved operability in detachably attaching the roller shaft.

[0080] The other end portion of the roller shaft may preferably have a stopper structure which is so configured as to keep the roller shaft from coming off the frame wall through the insertion hole formed in the frame wall unless an external force is applied, the stopper structure being detachably attachable to the sheet transporting device.

[0081] In the above arrangement, since the stopper structure enables to keep the roller shaft mounted between the frame walls from coming off the frame walls, there is no likelihood that the roller shaft may come off the frame walls during its rotation.

[0082] The stopper structure may preferably include a cutaway groove which is formed in a surface of the other end portion of the roller shaft, and a stopper ring which is detachably mounted in the cutaway groove.

[0083] In the above arrangement, the stopper ring is mounted in the cutaway groove of the roller shaft in a state that the roller shaft extends between the frame walls. This arrangement makes it possible to keep the roller shaft from axially displacing in such a direction as to come off the frame walls, namely from axially moving outwardly beyond the frame wall. Thus, there is no likelihood that the roller shaft may come off the frame walls.

[0084] In the above arrangement, in detaching the roller shaft from the frame walls, the operator is allowed to move the roller shaft in the axial direction of the roller shaft by simply detaching the stopper ring from the roller shaft, and thus, the roller shaft is detachable from the frame walls.

[0085] In this way, constituting the stopper structure by the cutaway groove formed in the roller shaft, and the stopper ring detachably mounted in the cutaway groove enables to securely keep the roller shaft from coming off the frame walls, while simplifying the stopper structure.

[0086] In the inventive sheet transporting device, rotation of the transmission gear is directly conveyed to the roller shaft without providing various parts of a complicated structure between the transmission gear and the roller shaft, which has been required in the conventional arrangement. This arrangement is advantageous in transmitting the rotation of the transmission gear without eccentric displacement of the roller shaft relative to the transmission gear, and in effectively preventing occurrence of a feeding-related trouble due to eccentric rotation of the feed roller.

[0087] Further, the number of parts can be remarkable reduced while simplifying the construction of the sheet transporting device, and to secure improved operability in detachably attaching the roller shaft.

[0088] This application is based on Japanese Patent Application No. 2003-153643 filed on May 30, 2003, the contents of which are hereby incorporated by reference.

[0089] Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein. 

What is claimed is:
 1. A sheet transporting device for use in an image forming apparatus comprising: a pair of frame walls opposed to each other; a roller shaft extending between the frame walls, opposite end portions of the roller shaft being received in insertion holes formed in the frame walls, respectively; a feed roller which is mounted on the roller shaft and is rotatable about an axis of the roller shaft, the feed roller for feeding sheets stacked on a sheet stacking portion of the image forming apparatus one by one from an uppermost sheet; a transmission gear which is provided at an outer side of one of the frame walls, the transmission gear having a center position opposed to the insertion hole of the frame wall; and an attachment structure which is so configured as to mount the roller shaft between the frame walls so as to transmit a driving force of the transmission gear to the roller shaft, the attachment structure including: a boss which is formed co-axially with the transmission gear and projects in the axial direction of the roller shaft to be received in the insertion hole of the frame wall, the boss being formed with a non-circular hole extending in the axial direction of the roller shaft; and an engaging end portion which is formed in an end portion of the roller shaft and has such a configuration as to be received in the non-circular hole of the boss in a non-rotatable state relative to the transmission gear.
 2. The sheet transporting device according to claim 1, wherein the other end portion of the roller shaft has a stopper structure which is so configured as to keep the roller shaft from coming off the frame wall through the insertion hole formed in the frame wall unless an external force is applied, the stopper structure being detachably attachable to the sheet transporting device.
 3. The sheet transporting device according to claim 2, wherein the stopper structure includes a cutaway groove which is formed in a surface of the other end portion of the roller shaft, and a stopper ring which is detachably mounted in the cutaway groove. 